As development across the United States continues to increase, the miles of roadway and number of stream crossings also increase. These roadways and crossings can have a potentially devastating effect on fish and wildlife in the area. Roadways often divide animal habitat, fragmenting populations and impeding migration patterns. While some wildlife passages have been implemented, they are still often inadequate or go unused due to the lack of natural vegetation and darkness in longer underground crossings. These wildlife passages, especially those for large mammals continue to become more important as the number of vehicle-animal incidents continues to increase.
The water stream crossings, which result as part of roadway development, are often inadequate because vegetation on the adjacent stream banks is shaded out and unable to grow. These shaded, barren stream banks no longer provide a habitat for aquatic life and discourage fish from moving upstream. In addition, the absence of vegetation may enhance scour or erosion problems due to the stream.
Thus, a significant limitation in culvert and bridge system design for environmentally sensitive areas is the changing of the natural habitat of streams, adjacent banks, and wildlife corridors. This alteration of the natural habitat can result in the elimination of plant growth and impede the migration of fish and wildlife in the area.
According to the Transportation Research Board (TRB) of the National Cooperative Highway Research Program, Project 25-27, FY 2004, “Every year, the costs of personal injuries and property damage resulting from animal/vehicle collisions are considerable. Various means have been employed to mitigate these collisions, with varying degrees of success. In recent years, highway agencies have placed a growing emphasis on protecting the environment. While many smaller species of animals do not pose a threat to vehicles through collisions, they experience significant habitat loss and fragmentation as a result of roadway alignments. Transportation corridors limit the natural movement of wildlife, affecting individual species and ecosystems.”